EP2125192A1

EP2125192A1 - Method and device for producing aromatic amines by heterogeneous catalyzed hydration

Info

Publication number: EP2125192A1
Application number: EP07711728A
Authority: EP
Inventors: Stephan Schubert; Ralph Schellen; Leslaw Mleczko; Stephan Laue; Peter Lehner
Original assignee: Bayer Technology Services GmbH
Current assignee: Bayer Intellectual Property GmbH
Priority date: 2006-03-14
Filing date: 2007-03-01
Publication date: 2009-12-02
Also published as: CN101400438A; US20090093655A1; RU2008140366A; BRPI0708889A2; WO2007104434A1; JP2009529549A; DE102006011497A1

Abstract

The invention relates to a method and a device for producing aromatic amines by heterogeneous catalyzed hydration, the catalyst required for the reaction being applied to the interior wall of one or more externally cooled reaction channels.

Description

Process and apparatus for the preparation of aromatic amines by a heterogeneously catalyzed hydrogenation

The invention relates to a process for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds in the presence of a catalyst applied to the inner wall of an externally cooled reaction channel.

Aromatic amines are important intermediates that need to be produced inexpensively in large quantities. For the economy of the process therefore high space-time yields and long catalyst life are crucial. The hydrogenation of nitroaromatics is a highly exothermic reaction. The removal and energetic use of the heat of reaction is therefore an important aspect in the production of aromatic amines.

For the gas-phase hydrogenation of nitroaromatics, various reactors are suitable. For example, No. 3,136,818 describes a process in which the reaction is carried out in a fluidized bed. The effective heat dissipation of this procedure is faced with problems due to the non-uniform residence time distribution (breakthrough of the nitroaromatics) and due to catalyst abrasion.

Other methods use fixed catalysts in fixed beds. With this arrangement, the reaction can be carried out with very narrow residence time distribution and circumventing the problem of catalyst abrasion. However, a known technical problem here is the formation of hot spots, i. local overheating in the fixed bed catalyst. These lead to an increased deactivation of the catalyst by coking and can also permanently damage the catalyst in extreme cases.

In an adiabatic operation of the fixed bed reactor, the problem of heat dissipation is bypassed by the heat released is completely absorbed by the gas stream. Such a method, which is characterized by a simple construction and easy scalability of the individual apparatuses, is e.g. in EP 0 696 574. However, in order to keep the adiabatic temperature rise within limits, very large gas flows must be recirculated in the adiabatic mode of operation.

DE2849002 describes a process for the reduction of nitro compounds in the presence of stationary, palladium-containing multicomponent supported catalysts in cooled shell-and-tube reactors. The contact consists essentially of 1 to 20 g of palladium, 1 to 20 g of vanadium and 1 to 20 g of lead per liter of CX-Al ₂ O ₃ . It has proved to be advantageous if the active components as close to the surface of the catalyst in a very sharp Zone are present depressed and inside the support material, no active components are included. A disadvantage of the gas phase hydrogenation described in DE 2 849 002 is the low specific loading of the catalysts, which is essentially due to insufficient heat removal. The specified loads are about 0.4 to 0.5 kg / (lh). The load is defined as the amount of nitroaromatics in kg, which is enforced per liter of catalyst charge within one hour. Associated with the low catalyst loading is an unsatisfactory space-time yield in industrial processes for the production of aromatic amines. Furthermore, the selectivities at the beginning of a driving period are significantly lower than towards the end, which leads to yield losses and problems in the workup of the crude product.

The load on the catalyst can only be increased in isothermal reactors if the heat released during the reaction can be efficiently removed. WO 98/25881 describes the use of inert materials for diluting the catalyst bed in the preparation of aromatic amines. The dilution enlarges the reaction zone and thus increases the area available for heat exchange. With this procedure, the hot spot temperature can be lowered or the potential nitroaromatic load can be increased at a constant hot spot temperature. Due to the dilution, however, the service life of the bed decreases. In the example given in WO 98/25881, the productivity of the diluted bed was significantly lower than the productivity of the undiluted bed owing to the short service lives despite higher loading.

Klemm et al. describe in Chemical Engineering Science 56 (2001) pp. 1347 - 1353 the preparation of a catalytic laboratory wall reactor for the determination of the deactivation kinetics of the catalytic hydrogenation of nitrobenzene to aniline. The direct application of the 100 .mu.m-400 .mu.m thick catalyst layer to the inner wall of an externally cooled metal tube with an internal diameter of 10 mm allows isothermal reaction conditions to be achieved. However, a scale-up of the Wanderactors described with individually coated and then assembled into a large-scale reactor pipes is not practical. Another disadvantage of the wall reactor described is the low volume fraction of 4% -15%, which would lead to very large reactor dimensions in the case of large-scale implementation of the concept.

DE 1 0347 439 describes a process for the preparation of aromatic amines in which a catalyst is used which consists of a monolithic carrier and a thin catalytically active coating. It is advantageous here that a higher selectivity is achieved by the thin catalytically active layer than in comparable fixed beds can. The disadvantage, however, is that the monolithic supported catalyst described not cooled due to its poor radial heat dissipation from the outside but only adiabatic, ie usually with large gas flow in the circuit, which means a costly management of the process and other costs.

The object of the present invention is therefore to provide a process for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds, which reduces the formation of hotspots and allows a high space-time yield, longer life and higher selectivity.

The invention relates to a process for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds, which is characterized in that the catalyst required for the reaction is applied to the inner wall of one or more externally cooled reaction channels. Surprisingly, it has been found that in the method according to the invention the formation of hot spots during the process is effectively reduced, thereby allowing a higher space-time yield with likewise higher selectivity.

The cooling medium which is in thermal contact with the reaction channel is also preferably guided into at least two cooling medium channels which are essentially parallel to one another and which are conducted in direct current, countercurrent or crossflow in the reaction channel in relation to the main flow direction.

The cooling medium used is salt melts, steam, organic compounds or molten metals, preferably molten salts, steam or heat transfer oils, particularly preferably a mixture of potassium nitrate, sodium nitrite and sodium nitrate, dibenzyltoluene or a mixture of diphenyl oxide and diphenyl.

In a preferred embodiment of the method, the cooling medium or the cooling medium are conducted in the cross-flow to the main flow direction in the reaction channel. The cooling medium is usually divided into at least two substantially parallel cooling medium channels and the cooling medium channels can have different material properties, flow rates, flow rates or temperatures.

The catalyst is applied to the inner wall of the reaction channel in a 5 to 1000 .mu.m, preferably 10 to 500 .mu.m, more preferably 20 .mu.m to 200 .mu.m thick layer. The application can be carried out in principle by any known technology. Preference is given to using methods in which a plurality of reaction channels are coated by a single coating process with Ka be coated. Particularly preferred methods are used in which the catalyst is applied as a washcoat on the inner wall of the reaction channels. Usually, the catalyst is applied to the inner wall of at least two externally cooled reaction channels simultaneously.

The catalytically active coating for the hydrogenation of aromatic nitro compounds in the gas phase preferably contains metals from groups VIHa, Ib, IVa, Va, VIa, IVb and Vb of the Periodic Table of the Elements (Mendeleyev, Zeitschrift für Chemie 12, 405-6, 1869) as a catalytically active component. Preferred metals are Pd, Pt, Cu or Ni. The catalytically active component can be applied to a carrier. Suitable carrier substances are ceramic materials, such as, for example, Al ₂ O ₃ , SiO ₂ , TiO ₂ or zeolites, but also graphite or carbon. The carrier substance is preferably finely ground. In order to achieve a uniform coating, the volume-related particle size d _{90 of} the preferably milled carrier substance should preferably be less than 50 μm, more preferably less than 10 μm. The catalyst described in DE 2 849 002 is particularly preferably used as the catalytically active coating.

Preferably, at least two reaction channels are operated under the same reaction conditions.

For the method, the following inventive reactor, which itself is also the subject of the present application, suitable, without being limited thereto.

The reactor for the catalytic hydrogenation of aromatic nitro compounds according to the process of the invention consists of one or more externally cooled reaction channels, on the inner walls of which the catalyst required for the reaction is applied.

The proportion of the catalyst volume in the total volume of the device is usually from 1% to 50%, preferably from 5% to 35%, particularly preferably from 10% to 25%.

The reaction channels have a round or rectangular cross-sectional area with a hydraulic diameter, defined as a ratio of four times the internal cross-sectional area to the inner circumference, of 0.05 mm to 100 mm, preferably 0, 1 mm to 10 mm, particularly preferably 0.5 mm to 2 mm and a length of length of 0.02 m to 5.0 m, preferably 0.1 m to 1.0 m, particularly preferably 0.2 m to 0.7 m.

At least two, preferably from 20,000 to 200,000,000 reaction channels, preferably of the same geometry, are preferably arranged in parallel. In a particular embodiment, the reaction channels are arranged in one or more plates for reaction channels so that this plate is in thermal contact with at least one set of cooling medium channels arranged parallel, preferably also in one or more plates. At least two, more preferably 200 to 20,000 reaction channels per plate are arranged in parallel (FIG. 1). Furthermore, preferably at least two, more preferably 100 to 10,000, plates of reaction channels are arranged alternately one above the other, alternating with a comparable number of plates of cooling medium channels (FIGS. 2 and 3).

In a special embodiment of the reactor, the plates of reaction channels, which are arranged one above another in alternating fashion, and the cooling medium channels are subdivided into individual replaceable modules (FIGS. 4 and 5). In a particular embodiment of the method, at least two modules of superimposed planes of reaction channels and cooling medium channels are operated in parallel under the same reaction conditions, so that a single module can be removed from the process, added to the process or replaced without the operation of the other modules interrupt.

The temperature in the reaction channels is kept at as constant a temperature as possible by the cooling medium passages through which cooling medium flows. When using a temperature zone, this temperature is between 200 ⁰ C and 500 ⁰ C, preferably between 220 ⁰ C and 400 ⁰ C, more preferably between 24O ⁰ C and 330 ⁰ C.

The temperature of the reaction channel can be monitored by means of sensors during the process and the flow rate or the temperature of the cooling medium in the cooling medium channels can be adjusted as required. The sensors can be arranged either in the region of the cooling medium or in the region of the reaction channel, preferably in the inlet and outlet of the cooling medium.

The process according to the invention is preferably operated at pressures of from 1 to 30 bar, particularly preferably from 1 to 20 bar, very particularly preferably from 1 to 15 bar. The temperature of the Eduktgasgemischs is prior to the reactor inlet, preferably at 200 to 400 ⁰ C. Hydrogen and aromatic nitro compound to the reactor in a molar ratio of hydrogen to nitro group of preferably 3: supplied 1: 1 to 100th As the aromatic nitro compound, in particular those of the following formula can be hydrogenated:

wherein R and R _{2 are the} same or different and are hydrogen or C _r to C ₄ alkyl, in particular methyl and ethyl, and n = 1 or 2. Nitrobenzene or the isomeric nitrotoluenes are preferably hydrogenated by the process according to the invention.

The process can be carried out continuously or in batch, preferably continuously.

The process according to the invention can be carried out on an industrial scale. The space-time yield (kg of aniline per kg of catalyst and h) is between 0.1 and 100 kg / kg / h, preferably between 1 and 50 kg / kg / h and particularly preferably between 2 and 25 kg / kg / H.

The catalyst-coated reaction channel used according to the invention for the preparation of aromatic amines has significant advantages over conventional catalyst beds known from the prior art.

On the one hand, the pressure loss in the coated reaction channel at comparable flow rate is much lower than that of catalyst beds. Conversely, the coated reaction channel can be flowed through at the same pressure loss at much higher speeds.

On the other hand, due to the small thickness of the catalyst layer applied to the inner wall and the good heat transfer between the applied catalyst and the cooled by an outer cooling medium channel wall so high heat dissipation ensures that the reaction heat released by the reaction are immediately dissipated almost completely from the reaction channel thus avoiding hot spots and achieving longer service lives.

The very thin catalytically active coating also offers another advantage. If the catalytically active components are deposited in a very thin layer, the influence of diffusion is far less than with full catalysts. If the main reaction is accompanied by subsequent reactions, a higher selectivity can be achieved with these very thin catalytically active coatings. Application in a thin layer may also provide benefits in terms of value product selectivity.

Compared to the described prior art, the use of a immobilized catalyst, the use of a modular reactor concept (Figure 4), in which the cooled reactor consists of several parallel operated modules, advantageous. This design makes it possible to replace the modules individually when changing the catalyst and thus to significantly reduce production losses. By driving the remaining reactor modules at a higher load in the short term, the production loss can possibly also be partially or completely avoided become. Because of the ease of handling, the modular design of a microreactor is a particularly suitable and therefore preferred variant.

pictures:

Exemplary embodiments of the subject invention are shown in FIGS. 1 to 5 without being limited thereto.

Fig. 1: structured plate with parallel reaction channels (1).

Fig. 2: Module of alternately superimposed, structured plates for reaction channels (1) and cooling medium channels (2) in the cross flow.

Fig. 3: Cross-section of a module of alternately superimposed, structured plates for reaction channels (1) and cooling medium channels (2) in cocurrent or countercurrent.

Fig. 4: Arrangement of parallel operated, replaceable modules.

Fig. 5: Connections of the reaction channels and the cooling medium channels of two parallel operated modules that can be replaced without interrupting the operation of the other module.

Reference numerals:

1- reaction channels

2- cooling medium channels

3- Feed the reaction channels

4- removal of the reaction channels

5- Feed the cooling medium channels

6- Removal of cooling medium channels Examples:

The following examples illustrate the present invention without being limited thereto.

Example 1 (comparative example)

In a thermostated with oil (240 ⁰ C) reactor tube having an inner diameter of about 26 mm, 18 g of a corresponding to Example 1 in DE-A 28 49 002 Al manufactured catalyst, diluted with 43.7 g of SiC, filled. The dumping height was 300 mm. The temperature of the incoming reaction gas, consisting of 180 g of nitrobenzene per hour, 200 1 of hydrogen per hour and 100 1 of nitrogen per hour, was about 240 ⁰ C, the pressure corresponded to atmospheric pressure. The nitrobenzene conversion decreased continuously with time. The average conversion was at the set load of 10 g of nitrobenzene per g of catalyst per hour averaged over the first two hours 91.6%, which corresponds to a space-time yield of 13.8 g of aniline per kg of catalyst per hour. The mean selectivity during the period was 99.4%.

Example 2: Hydrogenation in a cooled catalyst-coated reaction channel

For the hydrogenation of nitrobenzene, two reactor modules thermostated with oil (240 ^° C.) were connected in series, each consisting of 28 reaction channels arranged in parallel. The reaction channels each had a length of 50 mm, a width of 0.5 mm and a height of 0.8 mm and were coated on the inside with a catalyst suitable for the hydrogenation of nitrobenzene. The starting base used was a catalyst prepared according to Example 1 in DE-A 28 49 002, which was ground to a particle size fraction with d ₉₀ <10 μm. The mass of immobilized catalyst was 78.2 mg in the first reactor module and 76.6 mg in the second reactor module. The temperature of the incoming reaction gas, consisting of 3 g nitrobenzene per hour and 6 ml of hydrogen per hour, was about 240 ⁰ C, the pressure corresponded to atmospheric pressure. The nitrobenzene conversion decreased continuously with time. The average conversion was 97.2% at the set load of 19.4 g nitrobenzene per g catalyst per hour averaged over the first two hours, giving a space-time yield of 28.4 g aniline per kg catalyst per hour equivalent. The mean selectivity during the period was 99.7%. The temperatures between the two reactor modules and after the second reactor module were measured continuously, with no increase in temperature was detected. Gas chromatograph analyzes of the products (average values of the first 2 h runtime)

Claims

claims:

1. A process for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds, characterized in that the catalyst required for the reaction is applied to the inner wall of one or more externally cooled reaction channels.

2. The method according to claim 1, characterized in that the standing with the reaction channel in thermal contact cooling medium to the main flow direction in the reaction channel in the DC, countercurrent or cross flow is performed.

3. The method according to claims 1 or 2, characterized in that the cooling medium is divided into at least two substantially parallel flow channels.

4. The method according to any one of claims 1 to 3, characterized in that one or more cooling medium to the main flow direction in the reaction channel are cross-flow, divided into at least two substantially parallel cooling medium channels and the cooling medium channels different material properties, flow rates, flow rates or Have temperatures.

5. The method according to any one of claims 1 to 4, characterized in that the catalyst applied to the inner wall of the reaction channel has a layer thickness of 5 microns to 1000 microns.

6. The method according to any one of claims 1 to 5, characterized in that the catalyst is applied simultaneously to the inner wall of at least two externally cooled reaction channels.

7. An apparatus for carrying out chemical reactions characterized in that it contains one or more cooled from the outside reaction channels, on the inner walls of a catalyst required for the reaction is applied.

8. The device according to claim 7, characterized in that the reaction channel has a round or rectangular cross-sectional area and a hydraulic diameter of 0.05 mm to 100 mm.

9. Device according to one of claims 7 or 8, characterized in that at least two reaction channels of the same geometry are arranged in parallel.

10. Device according to one of claims 7 to 9, characterized in that the reaction channels are arranged in a plane and that this plane is in thermal contact with at least one parallel arranged, cooling medium leading room.

11. Device according to one of claims 7 to 10, characterized in that the at least two levels of reaction channels are arranged alternately with cooling medium leading chambers parallel to each other.

12. Device according to one of claims 7 to 11, characterized in that the proportion of the catalyst volume in the total volume of the device is from 1% to 50%.